The overall goal of the proposed research will be to characterize, in a molecular and biological fashion, the genes encoding the members of the murine and human (CR1) gene family. This gene family include the CR1 and CR2 genes, and two new, previously undescribed gene. Additionally, the chromosomal location of human CR1 will be examined in relation to other linked genes sharing amino acid and nucleic acid homology to CR1. The mouse genome appears to contain at least four CR1/CR1- related genes which are expressed as mRNA transcripts in a variety of different tissues. The primary objective will be to clone and at least partially, if not completely, sequence these four genes and to characterize both biochemically and biologically the proteins encoded by these distinct genes. One of these genes is likely to be murine CR1 due to its tissue specific expression, nucleic acid homology to human CR1, and the size of it transcript. The other two genes appear not to encode CR1 or CR2, but instead two proteins expressed in tissues which suggest that they mat by either DAF or gp45-70, or other uncharacterized proteins. The proteins encoded by the CR1 gene family will be identified by: (i) using the cDNA sequences to produce recombinant protein in E. coli., (ii) using the recombinant protein to generate polyclonal antisera against the peptide sequence, (iii) analyzing the murine proteins identified by these antisera, and presuming the CR1-related genes share CR1/CR2-like activities, (iv) blocking the functions of the murine proteins by antibody binding, and (v) identifying the protein products of these genes by transfecting studies using the entire gene in either phage or cosmid vectors. Once the murine CR1-related genes have been identified, the human homologues will also be isolated and characterized. The linkage of the murine CR1 gene on murine chromosome 1 to SLE genes on chromosome 1 (gld and the NZB- linked SLE gene) will also be evaluated. The molecular linkage of human CR1, C4bp, and H, and perhaps the human homologue of the murine CR1-related gene Y, on human chromosome 1 will identify the second major complement protein locus (the C4 locus in the MHC would be the first) in the genome. The structure of the CR1 gene associated with the genetic instability of the region of the chromosome to which the CR1 gene maps suggests a mechanism for chromosomal instability which will be investigated.